1. Field of the Invention
The present invention relates to a low pressure gas discharge lamp having an inner electrode disposed in a tube and an outer electrode disposed on a surface of the tube.
2. Description of the Prior Art
In recent years, small gas discharge lamps have been used as parts of display devices.
More specifically, a light emitting tube composed of an extremely thin hollow glass tube is described in U.S. Pat. Nos. 4,645,979 and U.S. Pat. No. 4,871,941. A gas discharge lamp as described above has an inner electrode at one end of a rod shaped glass tube, which forms a slender discharge space, and a belt shaped outer electrode located along the axial direction of the outer surface of the tube. The lamp also has a phosphor layer which emits visible light coated on the inner surface of the tube. The phosphor is excited by U.V. radiation emitted from the filling gas, such as mercury vapor or xenon, due to a discharge generated between the inner electrode and the outer electrode. A lamp having a gas such as neon, which emitts visible light, is also described in the above publications.
However this lamp has an undesirable distribution of its brightness because the top portion of the tube, where the inner electrode is not provided, is darker than the other portions of the tube. The distribution of its brightness is improved by the art described in U.S. Pat. No. 4,887,002, but the brightness of the top portion of the tube is still lower than that of the other portions of the tube.